use cow_to_ascii_lowercase instead

[heygsc]

part of #761

https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_methods

If this PR can be merged, I will continue to use more cow methods in clippy.

[heygsc]

By the way, running clippy in make fix-format may cause some code to automatically change, which I did not submit because the clippy in make check-format allows it to pass.

These are not related to the methods I added, they already existed before. It seems that they don't need to be changed anymore?

[jaytaph]

By the way, running clippy in make fix-format may cause some code to automatically change, which I did not submit because the clippy in make check-format allows it to pass.

This is good. The PR should only reflect your changes, not unrelated format changes. I'm not sure why this is happening though.. The CI should automatically reject clippy issues that are not resolved, so everybody should have the same formatting. I've noticed this happens on occasion with other PR's, so it might be a good idea to look into this issue as well (later)..

[jaytaph]

Looks good.. Thanks @heygsc for the PR!

[jaytaph]

Ah, we found a small issue concerning your git commits. They need to be signed commits. For more info about signed commits see here: https://docs.github.com/authentication/managing-commit-signature-verification/about-commit-signature-verification

You should be able to either rebase your PR with a signed commit, or reopen a new PR with signed commits so we can merge.

[heygsc]

Okay, I did neglect to carefully read the contribution document. I only realized it before modifying the AUTHORS, so the second commit has a gpg sign.

I will open a new PR later.